On Sun, 1 Oct 2023 at 14:37, Tom Lane <t...@sss.pgh.pa.us> wrote: > I think what you're asking for is a scheme whereby some rows in a > table have datatype X in a particular column while other rows in > the very same physical table have datatype Y in the same column. > That is not happening, because there'd be no way to tell which > case applies to any particular row.
To be honest, I don't know enough about the postgresql on-disk format and tuple shape to be confident in how this would be solved. I was thinking more about the ergonomics of what would be helpful and wondering how viable it was. Sounds like not very viable. Rats. The docs [1] on changing column types include: > As an exception, when changing the type of an existing column, if the USING > clause does not change the column contents and the old type is either binary > coercible to the new type or an unconstrained domain over the new type, a > table rewrite is not needed ... and mention the specific case of switching between VARCHAR and TEXT not requiring a table or index rewrite. Seems like the specific case of int->bigint is impossible to make as easy, given the fixed sizes in the tuple and impossibility of knowing from tuple to tuple whether to read 4 or 8 bytes. regards, James [1] https://www.postgresql.org/docs/current/sql-altertable.html
